A Legacy Begins...

Creatures gain experience counters for each creature they destroy by combat. (all creatures start at level 0)

Level 1: remove 2 experience counters from target creature, that creature gets +1/+1 and vigilance
Level 2: Remove 5 experience counters from target creature (must be level 1 to do so), that creature gets +2/+1 and First Strike and Vigilance
Level 3: Remove 8 experience counter from target creature (must be level 2 to do so), that creature gets +3/+2 and First Strike, Trample, and Vigilance